Glutamine synthetase (GS) activity in chick ebryo brain and retina increases during the period of functional maturation of these nervous tissues and is, thus, a measure of their differentiated state. While the specific role of this enzyme in the onset of normal nervous activity remains unclear, recent studies have shown that high GS activities are associated with distinct brain nuclei actively processing visual signals. To clarify the normal function for GS, these nuclei will be isolated, their populations of neurons and non-neuronal cells separated and the subcellular distribution of the enzyme determined in each cell type. In brief, the proposals focus on the precise subcellular localization of GS as a measure of its major function. The investigations seek to determine the involvement of the enzyme with specific areas of developing brain and at least one neural pathway.